Today, we all use area codes. 720 area code is for Central Colorado, so are 970, 303 and 719. It’s 907 for Alaska, 302 for Delaware, 808 for Hawaii, so on and so forth. But do you know how they came in use? How they came into existence? Not many of us know that US Numbers were only seven digits before the advent of area codes! Yes, 303 rolled out in 1947 was the first area code, and 720 area code was added as an overlay for it in the late nineties.
The North American Numbering Plan, also called NANP came up with the idea to divide the territories of its countries as Numbering Plan Areas (NPAs), where each area can be determined using a three-digit code. This code is what we call area code. Rules don’t allow using 1 or 0 as the leading digit in an area code, as they are reserved as Central Office Codes. While 1 was originally ignored in switching equipment as a leading digit as it can’t be differentiated from loop disconnections, 0 was originally used for operator-assisted telephone calls.
Even the area codes assigned have reasoning behind them. For example, NPAs that have 9 as their second digit are usually reserved for format expansion in the future. Area codes that have two matching digits as their last two numbers like 755, are called ERC short for easily recognizable codes and hence reserved for existing requirements like Toll Free 800, 888, so on and so forth.
Also, area codes with a lot of subscribers and large volume of calls like NYC are usually given area codes that are easy to dial like 212. Even 720 area code is an overlay for 303, which is actually easy to remember and an original area code. Besides, area code 720 is also one of the largest calling zones in the Western US encompassing an area of more than 6000 miles to its credit! Wondering why easy to dial? Basically it was decided based on the pulse dialing system back then, where it was easier for operators to dial them. So area code 720 was not probably assigned thinking about the ease of dialing!
Different numbering plans are followed worldwide. In the US, numbering plans were strategized based on their zones that are identified with area codes. The zones are often divided further into subcategories or zones depending on the area and other factors. Sometimes, overlays like area code 720 may be added too. While area code 303 caters to Central part of Colorado, the numbers were close to being exhausted after previous divisions again in 1998, prompting the addition of area code 720 for the same zone as an overlay.
So when anyone sees 720 area code they would immediately know it’s Colorado, 212 New York, etc. Did you know besides area code 720, 303, 719 and 970 are also area codes for Colorado? Yes, 720 area code caters to a very large part of Colorado and among the very few zones where calls across that distance aren’t charged long-distance tariff.